Device and method for transmitting random access preamble

ABSTRACT

Base Station (BS) and User Equipment (UE) apparatuses for configuring a Random Access CHannel (RACH), and methods thereof, are provided. The method for a BS to configure a RACH includes generating configuration information on RACH resources, transmitting the configuration information on the RACH resources to a UE, receiving a random access preamble multiplexed on a plurality of continuous RACH resources from the UE, extracting the random access preamble multiplexed on the plurality of continuous RACH resources, and detecting the extracted random access preamble. The method for a UE to configure a RACH includes receiving configuration information on RACH resources from a BS, selecting occupied RACH resources among a plurality of continuous RACH resources, generating a random access preamble, multiplexing the generated random access preamble on the selected RACH resources, and transmitting the random access preamble on the selected RACH resources to the BS.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of a prior applicationSer. No. 14/539,393, filed on Nov. 12, 2014, a priori application Ser.No. 14/459,798, filed on Aug. 14, 2014, and of a prior U.S. NationalStage application Ser. No. 12/811,933, filed on Jul. 7, 2010, whichclaims the benefit under 35 U.S.C. §371 of an International applicationfiled on Jan. 7, 2009 and assigned application number PCT/KR2009/000051,which claims the benefit of a Chinese patent application filed on Jan.7, 2008 in the Chinese Intellectual Property Office and assigned Serialnumber 200810002414.2, the entire disclosure of each of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system. Moreparticularly, the present invention relates to a device and method fortransmitting a random access preamble in a wireless communicationsystem.

2. Description of the Related Art

Now, the 3rd Generation Mobile Communication System Partnership Project(3GPP) standardization organization has commenced on Long-term Evolution(LTE) to the existing system criteria. Among many physical layertransmission techniques, both a downlink transmission technique based onOrthogonal Frequency Division Multiplexing (OFDM) and an uplinktransmission technique based on Single Carrier Frequency DivisionMultiple Addressing (SCFDMA) are actively being researched.

In the following description, a sampling frequency of 30.72 MHz is usedas an example. In this case, when the interval between sub-carriers is15 KHz, the number of valid OFDM samples is 2048 and the correspondingsample interval is T_(s)=1/(15000×2048). For other sampling frequencies,the corresponding number of valid OFDM samples and the number of CyclicPrefix (CP) samples can be obtained in proportion to the samplingfrequency.

There are two types of a frame structure in an LTE system, namely aFrame Structure Type 1 and a Frame Structure Type 2. In Frame StructureType 1, a Frequency Division Duplex (FDD) mode is employed, and in aFrame Structure Type 2, a Time Division Duplex (TDD) mode is employed.Hereafter, the design of an LTE system implementing the Frame StructureType 2 with a TDD mode is described.

FIG. 1 illustrates a frame structure of an LTE TDD system according tothe related art.

Referring to FIG. 1, a radio frame with a length of 307200×T_(s)=10 msfor each radio frame is equally divided into two half-frames with alength of 153600×T_(s)=5 ms Each half-frame contains eight slots with alength of 15360T_(s)=0.5 ms and three special domains, i.e., theDownlink Pilot Time Slot (DwPTS), the Guard Period (GP) and the UplinkPilot Time Slot (UpPTS). The total combined length of the three specialdomains is 30720T_(s)=1 ms. Each slot contains several OFDM symbols.There are two kinds of CP in OFDM symbols, namely a general CP and anextended CP. A slot with the general CP contains 7 OFDM symbols and aslot with the extended CP contains 6 OFDM symbols. In the application ofgeneral CP, the CP in the first OFDM symbol of the slot is 160×T_(s)(about 5.21 μs) long, and the CPs in the remaining 6 OFDM symbols are144×T_(s) (4.69 μs) long. In the application of extended CP, the CP ineach OFDM symbols of the slot is 512×T_(s) (16.67 μs) long. Twocontinuous slots compose a subframe. Subframe 1 and subframe 6 containthe three special domains. According to the present discussion, subframe0, subframe 5 and the DwPTS are fixed for downlink transmission. Also,according to the present discussion, for the transition period of 5 ms,the UpPTS, subframe 2 and subframe 7 are fixed for uplink transmission.In addition, according to the present discussion, for the transitionperiod of 10 ms, the UpPTS and subframe 2 are fixed for uplinktransmission.

According to the present discussion on LTE TDD, the uplink data, therandom access preamble and the channel Sensing Reference Signal (SRS)can be transmitted in the UpPTS.

FIG. 2 illustrates a structure of a random access preamble according tothe related art.

Referring to FIG. 2, the random access preamble contains a circularprefix with a length of T_(CP) and a sequence with a length of T_(SEQ).Several structures of the preamble are defined in the table below:

TABLE 1 Parameters for the random access preamble The preamble formatT_(CP) T_(SEQ) 0  3152 × T_(s) 24576 × T_(s) 1 21012 × T_(s) 24576 ×T_(s) 2  6224 × T_(s) 2 × 24576 × T_(s) 3 21012 × T_(s) 2 × 24576 ×T_(s) 4   0 × T_(s)  4096 × T_(s) (only for the Frame Structure Type 2)

In Table 1, the preamble format 4 is only applied to an LTE TDD system,the sequence length T_(SEQ) of which is 4096×T_(s), which is equal tothe time length of two uplink SCFDMA symbols. Here, the CP lengthT_(CP), is 0, i.e., no CP is added in the preamble. The feature of sucha format is that the random access preamble is short and generallytransmitted by virtue of the UpPTS in an LTE TDD system. According tothe present discussion, a Random Access CHannel (RACH) signal, which isin this format, is transmitted in the position 5120×T_(s) prior to theend of UpPTS. Therefore, in the receiving end of a BS, the random accesspreamble is transmitted within the time segment with a length of5120×T_(s) prior to the end of UpPTS. Herein, a random access preambletransmitted through UpPTS is referred to as a short RACH.

According to the present discussion on LTE, the allocation of afrequency band for a Physical Uplink Control CHannel (PUCCH) isimplemented at the two ends of the band so as to avoid a Physical UplinkShared Data CHannel (PUSCH) being divided into multiple frequency bandsby the PUCCH. The reason for this is that user equipments transmittinguplink data through multiple frequency bands with no frequency overlapwill damage a single-carrier attribute, from which an increase of a CubeMetric (CM) results.

FIG. 3 schematically shows frequency locations of a RACH in an LTE FDDsystem according to the related art.

Referring to FIG. 3, in each RACH timing location, there are twopossible frequencies located at the two ends of the system frequencyband, which are adjacent to the PUCCH. This configuration is performedto avoid damaging the PUSCH's single-carrier attribute. According to thepresent discussion, in an LTE FDD system, only one RACH resource can beconfigured for one RACH's timing location. RACH's collision probabilityis controlled by configuring the RACH density in the time domain. Inorder to obtain the frequency diversity effect, the RACH implementsfrequency hopping between the two possible frequency locationsillustrated in FIG. 3. For an LTE TDD system, it is possible toconfigure several RACH resources for one RACH timing location tocounteract the limitation of an uplink downlink transition period.

It is a typical configuration that the UpPTS contains two SCFDMAsymbols. In this case, the UpPTS can be adopted to transmit either therandom access preamble in format 4 of Table 1 or the SRS. Suppose atleast one RACH resource has been configured in the UpPTS. To guaranteethat RACH resources are orthogonal to SRS resources, the SRS can only betransmitted through the rest of the frequency resources. Therefore, aneed exists for a RACH configuration method, wherein not only therequirement of the format 4 for the random access preamble can be met,but also the transmission of SRS can be implemented effectively.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a device and method for transmitting randomaccess preamble in a wireless communication system.

In accordance with an aspect of the present invention, a method for aBase Station (BS) to configure a Random Access CHannel (RACH) isprovided. The method includes generating configuration information onRACH resources, transmitting the configuration information on the RACHresources to a User Equipment (UE), receiving a random access preamblemultiplexed on a plurality of continuous RACH resources from the UE,extracting the random access preamble multiplexed on the plurality ofcontinuous RACH resources, and detecting the extracted random accesspreamble.

In accordance with another aspect of the present invention, a method forUE to configure a RACH is provided. The method includes receivingconfiguration information on RACH resources from a BS, selectingoccupied RACH resources among a plurality of continuous RACH resources,generating a random access preamble, multiplexing the generated randomaccess preamble on the selected RACH resources, and transmitting therandom access preamble on the selected RACH resources to the BS.

In accordance with yet another aspect of the present invention, a BSapparatus for configuring a RACH is provided. The apparatus includesbroadcast information generator for generating configuration informationon RACH resources, a transmitter for transmitting the configurationinformation on the RACH resources to a UE, a receiver for receiving arandom access preamble multiplexed on a plurality of continuous RACHresources from the UE, physical channel de-multiplexor for extractingthe random access preamble multiplexed on the plurality of continuousRACH resources, and a random access preamble for detecting the extractedrandom access preamble.

In accordance with still another aspect of the present invention, an UEapparatus for configuring a RACH is provided. The apparatus includes areceiver for receiving configuration information on RACH resources froma BS, a broadcast information interpreter for selecting occupied RACHresources among a plurality of continuous RACH resources, a randomaccess preamble generator for generating a random access preamble, aphysical channel multiplexor for multiplexing the generated randomaccess preamble on the selected RACH resources, and a transmitter fortransmitting the random access preamble on the selected RACH resourcesto the BS.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 shows a Long-term Evolution (LTE) Time Division Duplex (TDD)frame structure according to the related art;

FIG. 2 shows a structure of a random access preamble according to therelated art;

FIG. 3 shows a Random Access CHannel's (RACH's) location in thefrequency domain according to the related art;

FIG. 4 shows a device in a Base Station (BS) for RACH and SensingReference Signal (SRS) processing according to an exemplary embodimentof the present invention;

FIG. 5 shows a device in a User Equipment (UE) for RACH and SRSprocessing according to an exemplary embodiment of the presentinvention;

FIG. 6 shows a device in a BS for detecting several time divisionmultiplexed RACHs according to an exemplary embodiment of the presentinvention;

FIG. 7 shows a device in a UE for transmitting several time divisionmultiplexed RACHs according to an exemplary embodiment of the presentinvention;

FIG. 8 illustrates a method for configuring a RACH and a SRS accordingto an exemplary embodiment of the present invention;

FIG. 9 illustrates a method for configuring a RACH according to anexemplary embodiment of the present invention;

FIG. 10 illustrates a method for configuring a RACH in time divisionmultiplex mode according to an exemplary embodiment of the presentinvention; and

FIG. 11 shows a structure of a short RACH with a Cyclic Prefix (CP)according to an exemplary embodiment of the present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention are provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto at least one of such surfaces.

Exemplary embodiments of the present invention provide a method forconfiguring a Random Access CHannel (RACH) in a Long-term Evolution(LTE) Time Division Duplex (TDD) system. More specifically, exemplaryembodiments of the present invention provide a method for configuring arandom access preamble transmitted through an Uplink Pilot Time Slot(UpPTS). Hereinafter, the random access preamble transmitted through anUpPTS is referred to as a short RACH.

For an LTE TDD system, several RACH resources are configured in one RACHtiming location. Here, the RACH resource refers to a time frequencyresource with frequency bandwidth of R and time length T. In an LTEsystem, R=1.08 MHz and T refers to the time interval occupied by thepreamble. It is possible for a short RACH, which is transmitted throughan UpPTS, to carry a smaller number of preambles. For instance, in theLTE TDD system, 64 preambles are provided by the physical layer to layer2. If the number of preambles provided by each short RACH resource isless than 64, the physical layer configures a plurality of short RACHresources to obtain the ability to support 64 preambles. In addition, ifthe load of the RACH in the system is comparatively heavy, a pluralityof RACH resources are configured in one RACH timing location even thougheach RACH resource can provide 64 preambles.

Three methods for configuring the RACH are described below.

Method for Configuring a RACH and a Sensing Reference Signal (SRS)

Similar to the discussion on an LTE Frequency Division Duplex (FDD)system, in order to avoid damaging a Physical Uplink Shared DataChannel's (PUSCH)'s single-carrier attribute, only the frequencies onthe two ends of the system frequency band can be allocated as RACHresources for an LTE TDD system. More specifically, there are twosituations in the allocation. In one situation, a Physical UplinkControl CHannel (PUCCH) is configured in the two ends of the systemfrequency band. In this case, the two backup locations for RACHresources are the frequency resource adjacent to the PUCCH. In the othersituation, no PUCCH is configured in the two ends of the systemfrequency band. In this case, the two backup locations for RACHresources are the boundaries of the system frequency band.

Methods for allocating RACH resources in the RACH timing locations aredescribed below.

In the first method, a plurality of RACH resources are distributed inthe RACH backup resources at the two ends of the system frequency bandas uniformly as possible for one RACH timing location. Suppose that thenumber of RACH resources to be allocated at some RACH timing location isN, then

$\left\lfloor \frac{N}{2} \right\rfloor\mspace{14mu}{and}\mspace{14mu}\left\lceil \frac{N}{2} \right\rceil$RACH resources are respectively allocated at the two ends of the systemfrequency band. More specifically, if N=1, only one RACH resource isallocated at the RACH timing location and it is located at one end ofthe system frequency band. If N>1, at the RACH timing location, the RACHresources are distributed at the two ends of the system frequency bandas uniformly as possible. This method is applicable to all five formatsof the random access preamble listed in Table 1. With this method, RACHresources are uniformly distributed at the two ends of the frequencyband so as to be advantageous to frequency hopping resource allocationfor the PUSCH. An important frequency hopping method is the mirror imageone, wherein the RACH resources are uniformly distributed at the twoends of the frequency band to reduce the constraints on the PUSCHfrequency hopping. If the random access preamble is to be transmitted, aUser Equipment (UE) selects one occupied RACH resource among theplurality of RACH resources distributed at the two ends of the systemfrequency band according to the currently configured RACH resourcepatterns in a Base Station (BS), generates the random access preamble,and then multiplexes the generated preamble on the selected RACHresources for transmission. According to the currently configured RACHresource patterns, the BS extracts the random access preamble from theplurality of RACH resources distributed at the two ends of the systemfrequency band and then detects the extracted random access preamble.

In the second method, N₁ RACH resources are continuously distributed atone end of the system frequency band for one RACH timing location, andN₂ RACH resources are continuously distributed in the other end of thesystem frequency band for the next RACH timing location. Suppose thenumber of the RACH resources to be allocated at the two continuous RACHtiming locations is N₁ and N₂, respectively, and both of the N₁ and N₂are greater than or equal to 1. Here, the frequency domain distancebetween the RACH resources distributed in the two continuous RACH timinglocations can be guaranteed to be maximal so that the probability ofsuccessful retransmission of the random access preamble from UE can beimproved. If it is necessary to transmit the random access preamble, theUE selects one occupied RACH resource among the plurality of continuousRACH resources at one end of the system frequency band according to thecurrently configured RACH resource pattern in the BS, occupies theselected RACH resource, generates the random access preamble and thenmultiplexes the generated preamble on the selected RACH resource fortransmission. According to the currently configured RACH resourcepattern, the BS extracts the random access preamble among the pluralityof continuous RACH resources located at one end of the system frequencyband and then detects the extracted random access preamble.

The second method is applicable to all five formats of the random accesspreamble listed in Table 1. For instance, to allocate RACH resourceswithin the UpPTS with the second method, no constraint is performed onthe information transmitted through the frequencies rather than thoseoccupied by RACH resources, i.e., the information can be uplink data,SRS, or uplink control information, and the like. Here, suppose allfrequencies in UpPTS except for the one occupied by RACHs are adopted totransmit SRS. With the second method, the rest of the resources in theUpPTS form a continuous subfrequency channel that contains RACHs locateat two ends of the system frequency band, respectively. In this case, ifthe frequency band occupied by the RACH resource is narrower than orequal to one half of the system frequency band, the rest of theresources in two UpPTSs can cover the entire system bandwidth so thatthis method supports detection of all channels with differentfrequencies on the system bandwidth. For the rest of the resources, thenarrowband SRS can be transmitted, and if the bandwidth of broadband SRSis less than or equal to one half of the system bandwidth, the rest ofthe subfrequency bands within two UpPTS can support detection of abroadband channel for the entire system bandwidth. Moreover, if thebandwidth of the frequency band occupied by the RACH resources isgreater than one half of the system frequency band, this second methodsupports detection of a channel with frequencies covering as much of thesystem bandwidth as possible. The BS transmits the configurationinformation on SRS to the UE, and the UE transmits SRS via somefrequency in the rest of the subfrequency bands according to theconfiguration information transmitted by the BS.

For the first method mentioned above, if the number of the RACHresources to be allocated for the RACH timing location is more than two,several RACH resources are continuously allocated at one end of thesystem frequency band. For the second method mentioned above, if thenumber of the RACH resources to be allocated for the RACH timinglocation is more than 1, several RACH resources are continuouslyallocated at one end of the system frequency band. In general, in themethod for continuously allocating RACH resources, the adjacent RACHresources occupy adjacent Resource Blocks (RB). Suppose each RACHresource occupies R RBs. In this example, when some RACH resourceoccupies the k˜k+R−1 RBs, the adjacent RACH resource occupies thek−R˜k−1 RBs or the k+R˜k+2R−1 RBs. If interference between the RACHresources should be reduced, the process of continuously allocatingseveral RACH resources at one end of the system frequency band can beextended to allocate a plurality of RACH resources so that there are mRBs between adjacent RACH resources (m>=0). Here, m=0 corresponds to thecase of a method for normal continuous allocation. Suppose some RACHresource occupies the k˜k+R−1 RBs, then the adjacent RACH resourceoccupies the k−R−m˜k−1−m RBs or the k+R+m˜k+2R−1+m RBs.

The BS can indicate the currently configured RACH resource via thebroadcast channel. The system can predefine the configuration patternsfor some RACH resource. By indexing the configuration patterns, only theindex value is necessary to be transmitted via the broadcast channel.

FIG. 4 shows a device for processing a RACH and a SRS in a BS accordingto an exemplary embodiment of the present invention.

Referring to FIG. 4, the BS includes a broadcast information generator401 for generating broadcast information for configuring the RACH and aSRS configuration information generator 402 for generating SRSconfiguration information. The broadcast information and the SRSconfiguration information are multiplexed by a physical channelmultiplexer 403 to be transmitted through a transmitter/receiver 404.The BS receives a signal from a UE through the transmitter/receiver 404.The received signal is de-multiplexed through a physical channelde-multiplexer 405 according to the method proposed in exemplaryembodiments of the present invention. According to a currentlyconfigured pattern on RACH resources in the BS, the BS extracts a randomaccess preamble from the plurality of continuous RACH resources locatedat one end of the system frequency band and detects the extracted randomaccess preamble through a random access preamble detector 406. When theBS configures the frequencies other than those for RACH resources totransmit SRS, the BS extracts the SRS signal from the frequencies otherthan those for RACH resources and detects the extracted SRS through anSRS detector 407.

FIG. 5 shows a device for processing a RACH and a SRS in a UE accordingto an exemplary embodiment of the present invention.

Referring to FIG. 5, the UE receives a signal from a BS through atransmitter/receiver 504. The received signal is de-multiplexed througha physical channel de-multiplexer 503 and broadcast information on aRACH configuration is obtained by a Broadcast Information interpreter501 and SRS configuration information is obtained by a SRS configurationinformation interpreter 502. If it is necessary to transmit a randomaccess preamble, the UE selects its occupied RACH resources from theplurality of continuous resources at one end of the system frequencyband according to a currently configured RACH resource configurationpattern. The random access preamble is generated by a random accesspreamble generator 506. After being multiplexed by a physical channelmultiplexer 505 into the selected RACH resources, the preamble istransmitted through the transmitter/receiver means 504. In a case wherethe BS configures frequencies other than those for RACH resources totransmit SRS, the UE generates a SRS in SRS generator 507, multiplexesthe SRS into the BS's configured frequencies through the physicalchannel multiplexer 505, and transmits the SRS through thetransmitter/receiver 504.

Method for Configuring Multiple RACH Resources in UpPTS

In some configuration cases in an LTE TDD system, the UpPTS containsmore than two Single Carrier Frequency Division Multiple Addressing(SCFDMA) symbols. For instance, to be backward compatible with TimeDivision (TD)-SCDMA, the UpPTS can contain 2, 6, 7, or 11 symbols. Inthe preamble format 4 in Table 1, the time length is 5120×T_(s), whichis equal to a length of 2.5 SCFDMA symbols. Suppose some short RACHshave been transmitted via the UpPTS, then within the subfrequency bandfor RACH, the short RACHs only occupy part of the SCFDMA symbols. Forexample, when the UpPTS contains 6 symbols, three or four SCFDMA symbolswithin the subfrequency band for the RACH will be idle. A method isdescribed below on how to utilize these remaining time frequencyresources, according to an exemplary embodiment of the presentinvention.

If a plurality of RACH resources are configured in a UpPTS and the UpPTScontains comparatively many symbols, a solution of multiplexing aplurality of RACH resources in the UpPTS in a time division multiplexmode is provided, according to an exemplary embodiment of the presentinvention. Here, no constraint is declared on whether a BS is allowed toschedule resources occupied by RACHs to a UE for uplink datatransmission. If RACH resources should be guaranteed to be orthogonal toother resources (such as an SRS, uplink data, and the like), SCFDMAsymbols other than those for RACH in a subfrequency band should beadopted to transmit other information (such as the SRS, uplink data, andthe like). For instance, suppose that the time length of a short RACH isT. The time length of the preamble in format 4 in Table 1 for an LTE TDDsystem is 5120×T_(s), which is not an integer time of the length of thenumber of uplink symbols. The first method for allocating RACH resourcesin an UpPTS is to continuously allocate a plurality of RACH resources inthe subfrequency band for an RACH, i.e., the start sample of a latterRACH resource is the one next to the stop sample of the former RACHresource. For instance, the RACH resources are allocated continuouslyforward starting from a stop position of a UpPTS, or the RACH resourcesare allocated continuously backward starting from a start position ofthe UpPTS, or one RACH resource is allocated starting from stop positionof the second SCFDMA symbol in UpPTS, and other RACH resources areallocated continuously backward starting from the sampling position nextto the stop sample of the second SCFDMA symbol in UpPTS. The secondmethod for allocating RACH resources in UpPTS is to configure the RACHresources according to the boundaries of corresponding SCFDMA symbols.For instance, each RACH signal begins to be transmitted at a moment thatis T prior to the terminating position of its last SCFDMA symbol, oreach RACH signal begins to be transmitted at the moment when its firstSCFDMA symbol starts.

The method proposed in an exemplary embodiment of the present inventioncan be jointly used with a method for multiplexing a plurality of RACHresources based on Frequency Division Multiplexing (FDM). In this case,the RACH resources are allocated in several subfrequency bands of aUpPTS and at each subfrequency band, at least one RACH resource isallocated.

A BS can indicate the currently configured RACH resource via thebroadcast channel. The system can predefine some configuration patternsfor the RACH resource. By indexing the configuration patterns, only theindex value is necessary to be transmitted via the broadcast channel.

FIG. 6 shows a device with which a BS detects Time Division Multiplexed(TDM) RACH resources according to an exemplary embodiment of the presentinvention.

Referring to FIG. 6, the BS includes a broadcast information generator601 for generating broadcast information for configuring an RACH. Thebroadcast information is multiplexed by a physical channel multiplexer602, and transmitted through a transmitter/receiver 603. The BS receivesa signal through the transmitter/receiver 603 from a UE. The receivedsignal is de-multiplexed through a physical channel de-multiplexer 604according to a method proposed in an exemplary embodiment of the presentinvention. According to the currently configured RACH resource patterns,the BS extracts a random access preamble from the plurality of RACHresources multiplexed in a time division mode and detects the extractedrandom access preamble through a random access preamble detector 605.

FIG. 7 shows a device with which a UE transmits TDM RACH resourcesaccording to an exemplary embodiment of the present invention.

Referring to FIG. 7, the UE receives a signal from a BS through atransmitter/receiver 703. The received signal is de-multiplexed througha physical channel de-multiplexer 702 and a broadcast informationinterpreter 701 obtains broadcast information for configuring RACH. Ifit is necessary to transmit a random access preamble, a UE selects itsoccupied RACH resources among the plurality of TDM RACH resourcesaccording to currently configured RACH resource pattern and generates arandom access preamble in a random access preamble generator 705. Afterbeing multiplexed by a physical channel multiplexer 704 into theselected RACH resources, the preamble is transmitted through thetransmitter/receiver 703.

Structure of RACH Added with Cyclic Prefix (CP)

In format 4 of the random access preamble listed in Table 1, a length ofa CP is zero. To support the processing in the frequency domain, amethod based on overlap & add is adopted by a BS for receiving therandom access preamble. Configuring a general CP frame structure istaken as an example to describe a typical configuration of a UpPTS whenthe UpPTS contains two SCFDMA symbols. Suppose the symbol division andCP length setting within the lms period formed by the three specialdomains in the TDD system are substantially the same as that in othersubframes in a TDD system, the UpPTS is 4384×T_(s) long in the timedomain. In format 4, the preamble begins to transmit at a moment that is5120×T_(s) prior to the termination of the UpPTS. In this way, a RACHsignal in the preamble format 4 occupies part of a Guard Period (GP).Therefore, interference may easily be encountered from an adjacent BS'sdownlink signal when the RACH signal is transmitted in preamble format4. In more detail, since the RACH's initial timing is prior to theposition of the first symbol in the UpPTS, the RACH signal may haveencountered interference before any other signals transmitted throughthe frequencies other than those for the RACHs in the UpPTS thatencountered interference caused by the adjacent BS.

A method is described below for configuring the short RACH to addressthe interference problem mentioned above, according to an exemplaryembodiment of the present invention. One technique is to add a CP into aRACH signal, and the structures which are similar to the preambleformats 0-3 in table 1 are utilized. To guarantee that RACH signal'santi-interference performance is not less than that of other signalstransmitted through frequencies other than those for RACH signals inUpPTS, an exemplary embodiment of the present invention provides thatthe starting position of a Discrete Fourier Transform (DFT) window withwhich a BS detects the random access preamble is not earlier than thestart position of the first valid SCFDMA symbols starts in the UpPTS.Here, the start position of the valid SCFDMA symbol refers to the timingof the first SCFDMA sample without considering the CP. Suppose thelength of the CP in the first symbol of the UpPTS is C×T_(s), then thestarting position of the DFT window with which the BS detects the randomaccess preamble should be delayed at least C×T_(s) later than UpPTS'sinitial timing Taking the LTE TDD system as an example and supposingthat the symbol division and CP length setting within the lms periodformed by the three special domains are substantially the same as thatin other subframes, then according to a present LTE TDD subframestructure, C=160 when UpPTS contains 7 symbols, and otherwise, C=144.

The time lengths of a CP and a RACH signal's valid sequence can bedetermined according to such factors as the supported cell coverage, andthe like. When it is necessary to maintain the design parameters for thepreamble format 4, as shown in Table 2, one configuration method is toset the time length of the RACH signal's valid sequence asT_(p)=4096×T_(s) so as to be in accordance with the sequence length ofthe RACH signal in the preamble format 4. Suppose the RACH signals of anexemplary embodiment of the present invention begin to be transmitted atthe moment that is T prior to UpPTS's termination position. Forinstance, we can configure T=×5120T_(s) in the same mode for configuringthe RACH signal in the preamble format 4. The starting position of theDFT window for the BS detecting the random access preamble starts fromthe first valid SCFDMA symbol in UpPTS. In this case, the length of a CPin the RACH signal in an exemplary embodiment of present invention isT_(CP)=T−T_(p)−t_(cp), where t_(cP) denotes the length of the CP in thelast symbol of a UpPTS. For a general CP frame structure,t_(cp)=144×T_(s), and the length of CP is 880×T_(s).

TABLE 2 Format of preamble with added CP Preamble format T_(CP) T_(SEQ)x 880 × T_(s) 4096 × T_(s) (only applied to Frame Structure Type 2)

With this method, it is possible that the RACH preamble still occupiespart of the GP. However, the signal during such period is not utilizedby a BS when detecting the random access preamble. Also, with thismethod, the mitigation of interference caused by adjacent BSs isimproved. With this method, when the start position of the DFT windowwith which a BS detects the random access preamble is the start positionof the first valid SCFDMA symbol in a UpPTS, the RACH signal experiencesno interference until any other signals transmitted through the UpPTSsuffer from interference. When the start position of the DFT window withwhich BS detects the random access preamble is latter than the startposition of the first valid SCFDMA symbol in the UpPTS, the RACH signalsbegin to be interference only after any other signals transmittedthrough the UpPTS have suffered certain interference.

EXEMPLARY TECHNIQUES

In this section, four exemplary techniques are provided. To avoid tootedious a description of the four exemplary techniques, details ofwell-known functions or means are omitted.

First Exemplary Technique

A first exemplary technique to configure a plurality of RACH resourcesand a SRS in the UpPTS is described below. Consider a system with abandwidth of 5 MHz as an example and suppose the UpPTS contains twoSCFDMA symbols and there is no transmission of a PUCCH. Also, supposethat two RACH resources are transmitted in an FDM mode in an UpPTS, andthe rest of the resources in the UpPTS are adopted to transmit a SRS.Since the 5 MHz system contains 25 RBs and a bandwidth of each RACHresource occupies 6 RBs, only 13 other RBs exist in the UpPTS except forthe resources occupied by the RACH.

FIG. 8 illustrates a method for configuring a RACH and a SRS accordingto an exemplary embodiment of the present invention.

Referring to FIG. 8, in the first UpPTS, two RACH resources arecontinuously allocated from the upper end of the system frequency band,which occupies 12 RBs, and the remaining 13 RBs in the system bandwidthare adopted to transmit a SRS. In the second UpPTS, two RACH resourcesare continuously allocated from the lower end of the system frequencyband which occupies 12 RBs, and the remaining 13 RBs in the systembandwidth are adopted to transmit SRS. As shown in FIG. 8, the RACHresources in the second UpPTS are located respectively at the two endsof the system frequency band and can obtain superior frequency diversityeffect. Meanwhile, the SRS in the second UpPTS covers the entire systemfrequency band so that the measurement of a channel state over theentire system band is well supported. More particularly, this structurecan support the transmission of such narrowband SRSs as occupying abandwidth of 4 RBs or 6 RBs. Also, this structure can support thetransmission of such narrowband SRSs as occupying a width of 12 RBs or13 RBs, i.e., about half of the system bandwidth.

Second Exemplary Technique

A second exemplary technique for configuring a plurality of RACHresources in the preamble format 0 is described below for an LTE TDDsystem. Suppose the RACH channels are allocated in subframe 2 (orsubframe 5). Meanwhile, this subframe is adopted to transmit a PUCCH.Further suppose that one subframe is to transmit two RACH resources. Toextend the time length of the RACH resource to a plurality of subframes,this technique is also suitable for configuring the RACH resources inthe preamble formats 1˜3.

FIG. 9 illustrates a method for configuring a RACH according to anexemplary embodiment of the present invention.

Referring to FIG. 9, at least one RB at the two ends of the systemfrequency band is adopted to transmit a PUCCH. The two RACH resourceslocate in the two ends of the system band respectively and occupy theRBs adjacent to those for the PUCCH. Suppose that the PUCCH occupies kRBs, and the system bandwidth contains N RBs. If the RBs are indexedfrom 0, then k˜k+5 RBs are adopted to transmit one RACH resource, andthe N˜k−6˜N−k−1 RBs are adopted to transmit the other RACH resource. Inthis way, the mirror image relationship exists between the two RACHresources with respect to the center of the system bandwidth.Accordingly, the allocation of resources for a frequency hopping PUSCHwith the mirror image is not affected.

Third Exemplary Technique

A third exemplary technique for configuring a plurality of RACHresources in a UpPTS in a TDM mode is described below. Suppose the UpPTScontains 6 SCFDMA symbols and the two RACH resources can be accordinglymultiplexed together in the TDM mode. T denotes the length of timeoccupied by each RACH resource. For instance, the length of timeoccupied by the RACH resource in the preamble format 4 in Table 1 isT=5120×T_(s).

FIG. 10 illustrates a method for configuring a RACH in time divisionmultiplex mode according to an exemplary embodiment of the presentinvention. In order to highlight the third exemplary technique for TDMRACH resources, no illustration is done to the usage of frequenciesother than those for the RACHs in the UpPTS.

Referring to FIG. 10, in a first example, the two RACH resources arecontinuously allocated starting from the termination position of theUpPTS. In other words, the system begins to transmit RACH#1 at themoment that is T prior to the termination position of UpPTS, and thesystem begins to transmit RACH#0 at the moment that is 2T prior to thetermination position of UpPTS. Here, the first SCFDMA symbol in theUpPTS is not occupied by the RACH and therefore, the first SCFDMA symbolcan be adopted to transmit SRS or uplink data, and the like.

In a second example, the two RACH resources are continuously allocatedstarting from the start position of the UpPTS. In other words, thesystem begins to transmit RACH#0 at the moment of the start position ofUpPTS, and the system begins to transmit RACH#1 at the moment that isdelayed T behind the start position of UpPTS. Here, the last SCFDMAsymbol in the UpPTS is not occupied by the RACH and therefore can beadopted to transmit a SRS or uplink data, and the like.

In a third example, the two RACH resources are allocated starting fromthe stop position of SCFDMA symbol. In other words, the system begins totransmit RACH#0 at the moment that is T prior to the stop position ofthe second SCFDMA symbol in UpPTS, and the system begins to transmitRACH#1 at the moment that is T prior to the stop position of the fifthSCFDMA symbol in UpPTS. Here, the last SCFDMA symbol in the UpPTS is notoccupied by the RACH and therefore can be adopted to transmit SRS oruplink data, and the like.

In a fourth example, the two RACH resources are continuously allocated.In other words, the system begins to transmit RACH#0 at the moment thatis T prior to the stop position of the second SCFDMA symbol in UpPTS,and the system begins to transmit RACH#1 at the moment of the sampleposition next to the second SCFDMA symbol in the UpPTS. Here, the lastSCFDMA symbol in the UpPTS is not occupied by the RACH and therefore canbe adopted to transmit a SRS or uplink data, and the like.

In a fifth example, the two RACH resources are allocated both startingfrom the stop positions of the SCFDMA symbols. In other words, thesystem begins to transmit RACH#0 at the moment that is T prior to thestop position of the third SCFDMA symbol in UpPTS, and the system beginsto transmit RACH#1 at the moment that is T prior to the stop position ofthe sixth SCFDMA symbol in UpPTS.

Fourth Exemplary Technique

A fourth exemplary technique implementing a short RACH with an added CPis described below. Suppose the UpPTS contains two SCFDMA symbols andthe new short RACH structure is the same as the preamble format 4, i.e.,the system begins to transmit RACH at the moment that is 5120×T_(s)prior to the termination position of UpPTS.

FIG. 11 shows a structure of a short RACH with a CP according to anexemplary embodiment of the present invention.

Referring to FIG. 11 a configuration on the preamble with a CP isillustrated. With the preamble parameters in Table 2, the time length ofa RACH signal's sequence is 4096×T_(s), and the length of a CP is880×T_(s) The start position of the DFT with which a BS detects a randomaccess preamble is the start position of the first valid SCFDMA symbolin a UpPTS. With this technique, it is possible that the RACH preamblestill occupies part of the GP. However, since the signals within thisperiod are not utilized by the BS in the random access preambledetecting, the mitigation of interference caused by adjacent BSs isimproved. The RACH signal experiences substantially no interferencebefore any other signals transmitted through UpPTS suffer frominterference. With this configuration method, it is possible that theRACH signal causes interference to the first SCFDMA symbol of subframe 2(or subframe 6). But this interference level is very low.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting a random accesspreamble by a terminal in a wireless communication system employing timedivision duplex (TDD), the method comprising: receiving configurationinformation from a base station; identifying a plurality of randomaccess channel (RACH) resources in an uplink pilot time slot (UpPTS)based on the configuration information; selecting a RACH resource amongthe identified plurality of RACH resources; generating a random accesspreamble; transmitting the random access preamble using a first RACHresource of the plurality of RACH resources if the terminal transmitsthe random access preamble in a first time; and transmitting the randomaccess preamble using a second RACH resource of the plurality of RACHresources if the terminal transmits the random access preamble in asecond time, wherein the first RACH resource and the second RACHresource are configured to different positions in the UpPTS, and whereinthe first RACH resource and the second RACH resource are determinedbased on RACH resource frequency index.
 2. The method of claim 1,wherein the RACH resource occupies a bandwidth corresponding to 6consecutive resource blocks.
 3. The method of claim 1, wherein therandom access preamble is transmitted in an uplink pilot time slot(UpPTS).
 4. The method of claim 3, wherein a format for the randomaccess preamble transmitted in the UpPTS is
 4. 5. A method for receivinga random access preamble by a base station in a wireless communicationsystem employing time division duplex (TDD), the method comprising:generating configuration information to allocate a plurality of randomaccess channel (RACH) resources in an uplink pilot time slot (UpPTS),the plurality of RACH resources in the UpPTS are identified based on theconfiguration information; transmitting the configuration information toa terminal, a random access preamble being generated by the terminal;receiving the random access preamble using a first RACH resource of theplurality of RACH resources if the base station receives the randomaccess preamble in a first time; and receiving the random accesspreamble using a second RACH resource of the plurality of RACH resourcesif base station receives the random access preamble in a second time,wherein the first RACH resource and the second RACH resource areconfigured to different positions in the UpPTS, and wherein the firstRACH resource and the second RACH resource are determined based on RACHresource frequency index.
 6. The method of claim 5, wherein the RACHresource occupies a bandwidth corresponding to 6 consecutive resourceblocks.
 7. The method of claim 5, wherein the first random accesspreamble is received in an uplink pilot time slot (UpPTS).
 8. The methodof claim 7, wherein a format for the random access preamble received inthe UpPTS is
 4. 9. A terminal for transmitting a random access preamblein a wireless communication system employing time division duplex (TDD),the terminal comprising: a generator configured to generate a randomaccess preamble; and a transceiver configured to: receive configurationinformation from a base station, identify a plurality of random accesschannel (RACH) resources in an uplink pilot time slot (UpPTS) based onthe configuration information, select a RACH resource among theidentified plurality of RACH resources, transmit the random accesspreamble using a first RACH resource of the plurality of RACH resourcesif the terminal transmits the random access preamble in a first time,and transmit a sccond the random access preamble using a second RACHresource of the plurality of RACH resources if the terminal transmitsthe random access preamble in a second time, wherein the first RACHresource and the second RACH resource are configured to differentpositions in the UpPTS, and wherein the first RACH resource and thesecond RACH resource are determined based on RACH resource frequencyindex.
 10. The terminal of claim 9, wherein the RACH resource occupies abandwidth corresponding to 6 consecutive resource blocks.
 11. Theterminal of claim 9, wherein the random access preamble is transmittedin an uplink pilot time slot (UpPTS).
 12. The terminal of claim 11,wherein a format for the random access preamble transmitted in the UpPTSis
 4. 13. A base station for receiving a random access preamble in awireless communication system employing time division duplex (TDD), thebase station comprising: a generator configured to: generateconfiguration information to allocate a plurality of random accesschannel (RACH) resources in an uplink pilot time slot (UpPTS), theplurality of the RACH resources in the UpPTS being identified based onthe configuration information; and a transceiver configured to: transmitthe configuration information to a terminal, a random access preamblebeing generated by the terminal, receive the random access preambleusing a first RACH resource of the plurality of RACH resources if thebase station receives the random access preamble in a first time, andreceive the random access preamble using a second RACH resource of theplurality of RACH resources if base station receives the random accesspreamble in a second time, wherein the first RACH resource and thesecond RACH resource are configured to different positions in the UpPTS,and wherein the first RACH resource and the second RACH resource aredetermined based on RACH resource frequency index.
 14. The base stationof claim 13, wherein the RACH resource occupies a bandwidthcorresponding to 6 consecutive resource blocks.
 15. The base station ofclaim 13, wherein the first random access preamble is received in anuplink pilot time slot (UpPTS).
 16. The base station of claim 15,wherein a format for the random access preamble received in the UpPTS is4.